Rewritable mass memory media is typically contained in a rigid protective cartridge during operation and the cartridge typically includes a write-protect feature to protect information on a storage medium from being destroyed. For example, many data tape cartridges have a moveable plastic tab on the cartridge that can be moved to one of two positions. Similarly, flexible diskettes in hard plastic cases have a sliding or breakaway plastic tab on the plastic case. Rewritable compact disks (CD-RW) and rewritable Digital Versatile Disks (DVD, also called Digital Video Disks), however, are not in a cartridge during operation. Compact discs are commonly stored in clear plastic containers commonly called "jewel" cases or jewel boxes, but the disks are removed from these boxes during operation. Therefore, write protection for CD's and DVD's must be implemented directly on the disk medium. Solutions have been proposed that are software based. That is, if a particular bit or data field has a particular value, software (operating system or drive controller) is not supposed to overwrite data on the medium. However, software solutions require support by all operating systems, software drivers and drives. If a disk is created by one operating system or drive controller that supports a software write-protect feature, and then is taken to a system that does not support the feature, data may be inadvertently destroyed. In addition, a software virus could bypass software write protection to delete data on the disk. There is a need for a physical write-protect feature, directly on the disk medium, that protects against writing for any software or any drive.
Industry standard CD-RW media use a phase change material having a transparency that can be reversibly changed by heating, and then cooling at a controlled rate. In CD-RW drives, a laser is used to heat, and then cool small areas at a controlled rate. Laser power must be calibrated for each disk medium. Before writing or erasing, a standard CD-RW drive must successfully calibrate laser power by writing into a Power Calibration Area on the medium. If the drive cannot read the calibration patterns in the Power Calibration Area, it will not erase or write in the data area of the disk. U.S. application Ser. No. 08/823,823 discloses a write-protect device in which the Power Calibration Area is covered by a removable opaque adhesive backed ring. Optical disks of interest have a central hole. Drives grip the optical disk around the central hole using mechanisms that may be sensitive to the thickness of the optical disk. Therefore, the write protect ring preferably does not intrude in the area of the disk immediately surrounding the central hole in the disk. The permissible mechanical tolerance for positioning a write-protect ring is relatively small. However, if a write-protect ring cannot intrude into the area adjacent to the central hole in the disk, the central hole in the disk cannot be used to directly align a write-protect ring. There is a need for a low cost, easy-to-use system for precise positioning of adhesive backed write-protect rings onto optical disks.